1. Field of the Invention
The present invention generally relates to milling jars. More specifically, the present invention relates to a milling jar with integrated lifters.
2. Description of the Related Art
Jar mills are commonly employed for mixing, sifting, grinding, and/or polishing raw materials. A mechanical jar mill consists of at least one pair of parallel rollers horizontally mounted to a frame. The rollers are operated by motors, which cause the rollers to rotate in the same direction at variable speeds. A milling jar is placed on top of the rotating rollers, which rotate the milling jar. Generally, a suspension consisting of particulate materials in a liquid is placed inside the milling jar.
When the milling jar is rotated at the correct speed, the force inside the milling jar keeps the particulate materials against the jar wall as it rotates, and gravity will pull the particulate materials from the wall and cause the particulate materials to fall before the jar has spun an entire rotation. Abrasion or friction between the particulate materials causes the desired mixing, sifting, grinding, and/or polishing.
If the milling jar is rotated too quickly, the force keeping the particulate materials against the jar wall will be stronger than gravity, thereby causing the particulate materials to remain against the jar wall for an entire rotation. As a result, there will be no friction between the particulate materials. This is known in the art as “centrifuging.” If the jar is rotated too slowly, the force will not be strong enough to keep the particulate materials against the jar wall, and gravity will cause them to remain at the bottom of the jar. Again, the absence of friction will prevent the particulate materials from being mixed, sifted, polished, and/or ground.
To prevent problems associated with rotation speed, lifter bars are often placed inside the milling jars at 90 degree angles to the jar walls. Some of the particulate materials collect on the bars and are lifted upwards as the milling jar rotates between 0 and 180 degrees, and then fall from the bars due to gravity when the milling jar rotates between 180 and 360 degrees. Additionally, baffles are sometimes placed inside milling jars to help direct the flow of the materials. However, the placement of lifter bars and baffles on the interior of the milling jars is cumbersome. Removing particulate materials from the jar after the milling process is complete is also difficult. Moreover, use of these devices does not promote constant movement of the particulate materials inside the milling jars because some of the particulate materials get caught on the sharp edges of the lifting bars or baffles.
Therefore, there is a need for a milling jar having axial lifters with smooth surfaces that are integrated into the jar walls during the casting process.